Measuring fluid level in tank with complex geometrical shape

Abstract

A system and method for efficiently measuring the fluid level in a container having a non-uniform cross sectional area is described. The measuring device may be immersed in the fluid and have a float slidable along a structure having the capability to sense an aspect of the location of the float. Since the accuracy requirements in measuring the fluid level may be more important for the higher levels and the lower levels than the intermediate quantities, the sensor may likewise be configured to provide more accurate measurements near the upper and lower fill levels. The position of a float may be determined by capacitive optical or magnetic sensing techniques and the sensed position translated into engineering units for output by a calibration table.

1 . A device for measuring a level of a fluid in a reservoir, comprising:
 a structure having a plurality of sensor elements mounted along a vertical direction thereof; and   an object to be sensed, constrained to move along the vertical direction of the structure without binding in response to a change in fluid level in the reservoir and spaced apart therefrom,   each sensing element of the plurality of sensor elements capable of detecting the object to be sensed when a sensed portion of the object is disposed so as to oppose the sensing element; and the object to be sensed is configured to be sensed by at least one sensor element,   wherein the structure has an arcuate shape and is sized and dimensioned to mount internal to the reservoir, the reservoir comprising a first arcuate surface whose radius of curvature conforms to a radius of curvature of an adjacent first cylindrical surface and a second arcuate surface whose radius conforms to a radius of curvature of an adjacent second cylindrical surface.   
     
     
         2 . The device of  claim 1 , wherein a status of each sensing element is determined by a processor and the processor executes a program stored in a non-volatile computer readable medium to:
 determine that one or more sensor elements of the plurality of sensor elements has sensed the object; and   select a location value to be output,   wherein the location value to be output is a vertical location of the sensor element when one of the plurality of sensor elements has sensed the object to be sensed; or, when more than one sensing element of the plurality of sensing elements has sensed the object, the location value is a vertical location of the sensor element of the plurality of sensor elements that has sensed the object and is closest to an end of the structure.   
     
     
         3 . The device of  claim 1 , wherein a relationship between a location along the vertical direction and a quantity of fluid is determined for the reservoir in which the structure having the plurality of sensor elements is fixedly mounted, and a vertical location value to be output is converted to a fluid quantity using a predetermined relationship between a sensor output of the sensor element and a fluid quantity at the location of the sensing corresponding to the location value output. 
     
     
         4 . The device of  claim 1 , wherein a relationship between a vertical location value and a quantity of fluid in the reservoir is determined and stored in a non-volatile memory. 
     
     
         5 . The device of  claim 2 , wherein the sensing element further comprises:
 a plurality of pairs of metal plates arranged on or near a surface of the structure, where the structure is a non-conducting material and the object to be sensed has a metallic strip constrained to be movably disposed opposite the plurality of sensing elements and having a length extending in a transverse direction of the structure.   
     
     
         6 . The device of  claim 5 , wherein the pairs of metal plates are spaced apart in the vertical direction of the structure by a variable linear spacing; and a capacitance value of each of the pairs of metal plates is measured by a processor; and
 the processor configured to execute computer-readable instructions stored in a non-volatile memory to determine a state of the pair of metal plates based on a comparison of measured capacitance value with a capacitance value threshold for each of the pairs of metal plates.   
     
     
         7 . The device of  claim 2 , wherein a plurality of metal plates is arranged in a column along the vertical direction of the structure by a variable spacing; and the processor measures a capacitance of adjacent metal plates in the column; and
 a state of each of pairs of adjacent metal plates of the plurality of metal plates is determined by the processor based on a comparison of the measured capacitance of each pair of adjacent metal plates with a capacitance threshold for each adjacent pair of metal plates in the column.   
     
     
         8 . The device of  claim 3 , wherein the sensor element is a retro-reflective optical sensor and the element to be sensed is a diffuse reflector or a retroreflector strip. 
     
     
         9 . The device of  claim 8 , wherein the element to be sensed is a linear strip adhered to the object to be sensed. 
     
     
         10 . A method of determining a level of a fluid in a reservoir, comprising:
 providing a structure having a plurality of sensor elements mounted along a vertical direction,   wherein the structure has an arcuate shape and is sized and dimensioned to mount internal to the reservoir comprising a first arcuate surface whose radius of curvature conforms to a radius of curvature of an adjacent first cylindrical surface and a second arcuate surface whose radius conforms to a radius of curvature of an adjacent second arcuate cylindrical surface;   providing an object to be sensed, constrained to move along the vertical direction of the structure and spaced apart therefrom, the object having a smaller specific gravity than a specific gravity of the fluid; and   a processor configured to execute a program stored in a non-volatile computer-readable medium,   wherein a linear spacing between adjacent sensors along the vertical direction is varied between an upper distance limit and a lower distance limit; and a sensed portion of the object to be sensed has an extent in the vertical direction that is at least as great as the upper distance limit;   the method further comprising:   determining, by the processor, that one or more of the sensor elements has sensed the sensed portion of the object; and   outputting a location value representing a vertical position of the sensed portion of the object,   wherein the location value is a location of the sensor when the sensed portion of the object is sensed by a single sensor, or the location value is the location of the sensor having a smallest linear spacing to an adjacent sensor and closest to an end of the structure when the sensed portion of the object is sensed by more than one sensor.   
     
     
         11 . The method of  claim 10 , further comprising:
 determining a relationship between the location value and a volume quantity of the fluid in the reservoir; and   converting the location value to engineering units to be output.   
     
     
         12 . The method of  claim 10 , further comprising determining a relationship between the location value and a quantity of the fluid in the reservoir; and
 converting the location value to alphanumeric indications.   
     
     
         13 . The method of  claim 10 , further comprising:
 setting a predetermined maximum level of fluid permitted in the reservoir and a predetermined minimum level of fluid permitted in the reservoir; and   the processor configured to control adding fluid to the reservoir when the predetermined minimum level of fluid is determined and to cease adding fluid to the reservoir when the predetermined maximum level of fluid is determined.   
     
     
         14 . The method of  claim 10 , wherein a sensor element of the plurality of sensors further comprises:
 a plurality of pairs of metal plates arranged on or near a surface of the structure, and where the object to be sensed comprises a metal strip constrained to move in a vertical direction corresponding to a level of the fluid, dimensioned such that when the metal strip is disposed opposite the pair of metal plates, the metal strip opposes both of the plates of the pair of plates.   
     
     
         15 . The method of  claim 10 , wherein a sensor element of the plurality of sensors comprises pairs of metal plates spaced apart in a direction transverse to the vertical direction of the structure; and a capacitance value of each of the pairs of metal plates is measured by a processor; and
 the processor configured to execute computer-readable instructions stored in a non-volatile memory to determine a state of the pair of metal plates based on a comparison of measured capacitance value with a capacitance value threshold for each of the pair of metal plates.   
     
     
         16 . The method of  claim 10 , wherein a sensor element of the plurality of sensors comprises metal plates spaced apart in a column in the vertical direction of the structure spacing; and a capacitance value of each of pair of metal plates in the column, taken as a pair, is measured by a processor; and
 the processor configured to execute computer-readable instructions stored in a non-volatile memory to determine a state of pairs of metal plates based on a comparison of measured capacitance value with a predetermined capacitance value threshold for each of pair of metal plates.